1. Field of the Invention
The present invention relates to a method for allowing a control of a vehicle provided with at least two wheels in case of puncture of a tyre.
2. Description of the Related Art
A wheel for a two- or four-wheeled vehicle generally comprises a rim coupled with a tyre that is inflated to a given operating pressure.
Said tyre generally comprises a carcass structure having at least one carcass ply and at least one annular reinforcing structure associated with the carcass ply, a tread band of elastomer material applied to the carcass structure at a radially external position, a belt structure interposed between the carcass structure and the tread band and a pair of sidewalls at axially opposite positions on the carcass structure.
In tubeless tyres, the tyre airtightness is ensured by the radially internal layer of said carcass structure generally referred to as “liner”. In use, due to the natural air leakage through said liner (which in any case is never perfectly impervious to air), pressure within the tyre decreases so that the vehicle's driver is forced to carry out a periodical restoration of said pressure.
In an attempt to make the tyre pressure substantially constant over a rather long period of time, use of rims internally housing a tank containing a fluid under pressure (such as air, nitrogen or other substantially inert gases) has been suggested, in which tank there is a pressure higher than the operating pressure of the tyre. By means of one or more valves suitably operated, the required pressure is restored when needed.
U.S. Pat. No. 4,067,376 shows an alarm system connected with the pressure in a tyre which comprises a pressure-sensitive device susceptible of being mounted to the wheel and suitable to emit sonic or ultrasonic signals each time the inner pressure of the tyre exceeds a maximum value or is lower than a minimum value. Also shown is a system for automatically reintroducing the air lost by a tyre while a vehicle is running, to minimise the effects of a burst. Manufacture of the wheel involves the presence of an integrated annular bag suitable to store an amount of compressed air under high pressure. A safety pressure valve is placed between said bag and the tyre and is adapted to release air from the bag to the tyre each time pressure in the tyre goes down below a predetermined limit.
The Applicant realised that known devices, those of the previously illustrated type for example, do not allow the driver to be warned about a possible puncture in due time so as to enable him/her to stop the vehicle without consequences for the driver himself/herself and the passengers, if any. More specifically, said devices do not ensure a sufficient margin of safety enabling the vehicle to be stopped before the latter becomes uncontrollable due to a sudden lowering of the inner pressure in the tyre.
In particular, it is the Applicant's perception that a margin of safety can be conveniently obtained not only when the inner pressure of the punctured tyre is maintained to a value sufficient to enable running of the tyre for a suitable period of time, due to a quick admission of air into the tyre itself, but also when the driver is rapidly made acquainted with a danger situation.
In a two-wheeled vehicle this aspect is of vital importance for the rider's safety because due to the particular dynamics of this vehicle, the rider can become acquainted with such a situation too late.
In fact, in comparison with tyres for four-wheeled vehicles, quite particular performances involving many structural differences are required from tyres for two-wheeled vehicles. The most important differences originate from the fact that during running on a bend a motorcycle must remarkably tilt with respect to the position during a straight run, forming an angle (called camber angle) with the perpendicular to the ground that can reach 45° and, under extreme drive conditions, 65°.
Therefore, when a motorcycle faces a bend, the ground-contact area of the tyre progressively moves from the central region of the tread towards the axially outermost region in the direction of the bend centre. For this reason tyres for two-wheeled vehicles are distinguishable for their marked transverse curvature. This transverse curvature is usually defined by the particular value of the ratio of the distance between the radially outer point of the tread and the line passing through the laterally opposite extremities of the tread itself measured on the equatorial plane of the tyre, to the distance measured along the tyre chord between said extremities. In tyres for two-wheeled vehicles, the value of the curvature ratio is generally not lower than 0.15 and is normally in the order of about 0.3 for rear tyres, but also higher, until about 0.45, for front tyres, against a value usually in the order of about 0.05 in tyres for motor-vehicles.
The foregoing being stated, it is to be pointed out that the effects of a quick deflation of the tyres in two-wheeled medium-powered or high-powered vehicles, and in particular in maxi-scooters of the new generation, are very dangerous in terms of incidence on the loss of control of the vehicle, irrespective of the running speed.
More specifically, in case of deflation of the rear tyre a very quick starting of oscillations in the rear axle occurs, which oscillations are amplified until the vehicle becomes uncontrollable. In the case of a full-load configuration and with a passenger the tyre unbeading can occur, which has important consequences for the rider and the passenger.
These effects can be more easily detected on two-wheeled vehicles such as maxi-scooters, due to the strong load on the rear axle connected with positioning of the propeller. For this type of vehicles the danger level is still higher when the engine is of the balancing type and is therefore an integral part of the suspension, because this gives rise to a high value of the oscillating unsprung mass.
When deflation of a front tyre occurs, in addition to the above described effects there are also depreciatory effects on the drive features, since driving becomes harder and this difficulty suddenly appears on a bend when there is a resistance to a variation of the camber angle which will bring about the very dangerous effect of occupying the opposite ride lane.
Although in a car the effects of a quick deflation of a tyre are not as critical as in the case of a two-wheeled vehicle, they are however very dangerous both for the vehicle that, due to an “out-of-control”, can be seriously damaged, and for the driver and the passengers that, even though well protected by the vehicle bodywork and the modern safety systems (such as pre-tensioning of the belts, airbags, bars against intrusion on the structure), are in any case exposed to injuries and lesions that can also be very serious depending on the impact velocity.